The present invention relates to heat packs, and relates more particularly to such a heat pack which is capable of being recharged by microwave energy.
Heat packs which utilize saturated sodium acetate solution that can be activated to liberate heat have become increasingly popular in recent years. Exemplar of these heat packs can be seen in U.S. Pat. No. 4,077,390. U.S. Pat. No. 4,880,953 teaches a method of recharging or regenerating a substantially solid spent heat pack of the type in which a super-coolable salt solution is confined within a flexible plastic pouch and converted to solid form with evolution of heat, by contacting the solid contents of the pack with a source of microwave energy sufficient to melt the solid to the liquid state, without thereby damaging the heat pack. However, the heat pack used in U.S. Pat. No. 4,880,953 does not allow internal welds to be made between the two opposite side walls of the flexible plastic pouch. Furthermore, because the activator is a metallic means, it tends to reflect microwave energy onto a limited area to regenerate the spent heat pack.